Microstructure and EMW absorbing properties of SiCnw/SiBCN-Si3N4 ceramics annealed at different temperatures

SiC nanowire/siliconboron carbonitride-Silicon nitride (SiCnw/SiBCN-Si3N4) ceramics were prepared via a low-pressure chemical vapor deposition and infiltration (LPCVD/CVI) technique. The as-prepared ceramics were annealed at varying temperatures (1200-1600 degrees C) in a N-2 atmosphere, and their crystallization mechanism and absorbing properties were subsequently studied. The absorbing properties of the SiCnw/SiBCN-Si3N4 ceramics improved with the annealing temperature up to a certain value and decreased thereafter. Among the samples tested, the SiCnw/SiBCN-Si3N4 ceramics annealed at 1300 degrees C showed the highest permittivity (real and imaginary parts) and dielectric loss values in the X-band (ca. 5.34, 2.55, and 0.47 respectively), and this could be attributed to the precipitation of carbon and SiC nanocrystals. The sample treated at 1300 degrees C decreased its minimum reflection coefficient (RC) from -12.0 to -59.68 dB (compared with the as-received SiCnw/SiBCN-Si3N4 ceramics) and the effective RC (below -10 dB) in the whole X-band could be achieved when the thickness was set to 3-3.5 mm. These results revealed that the absorbing performance was significantly improved after the heat treatment at 1300 degrees C.